U.S. patent number 10,557,341 [Application Number 15/358,891] was granted by the patent office on 2020-02-11 for methods of evaluating cement isolations and quality.
This patent grant is currently assigned to SCHLUMBERGER TECHNOLOGY CORPORATION. The grantee listed for this patent is SCHLUMBERGER TECHNOLOGY CORPORATION. Invention is credited to Gunnar Gerard De Bruijn, Philippe Enkababian, Polina Khalilova, Petr Kolchanov, Jesse Lee, Jean-Paul Mogou Dessap, Olivier Naud, Dmitriy Potapenko, Larry Charles Todd.
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United States Patent |
10,557,341 |
Kolchanov , et al. |
February 11, 2020 |
Methods of evaluating cement isolations and quality
Abstract
A method may include preparing a map of cement quality for one
or more intervals of a wellbore; determining anticipated regions of
fluid communication and anticipated regions of zonal isolation from
the map of cement quality; and designing a stimulating treatment
based on the presence of regions of fluid communication.
Inventors: |
Kolchanov; Petr (Sugar Land,
TX), De Bruijn; Gunnar Gerard (Houston, TX), Potapenko;
Dmitriy (Sugar Land, TX), Lee; Jesse (Sugar Land,
TX), Khalilova; Polina (Houston, TX), Todd; Larry
Charles (Magnolia, TX), Enkababian; Philippe (Richmond,
TX), Naud; Olivier (Cheraga, DZ), Mogou Dessap;
Jean-Paul (Houston, TX) |
Applicant: |
Name |
City |
State |
Country |
Type |
SCHLUMBERGER TECHNOLOGY CORPORATION |
Sugar Land |
TX |
US |
|
|
Assignee: |
SCHLUMBERGER TECHNOLOGY
CORPORATION (Sugar Land, TX)
|
Family
ID: |
62144309 |
Appl.
No.: |
15/358,891 |
Filed: |
November 22, 2016 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20180142544 A1 |
May 24, 2018 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
E21B
47/005 (20200501); G06F 30/20 (20200101); E21B
33/14 (20130101); E21B 43/25 (20130101) |
Current International
Class: |
E21B
47/005 (20120101); E21B 47/00 (20120101); E21B
33/14 (20060101); E21B 43/25 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Harcourt; Brad
Attorney, Agent or Firm: Tran; Andrea E.
Claims
What is claimed is:
1. A method comprising: preparing a map of cement quality for one
or more intervals of a wellbore; determining anticipated regions of
fluid communication and anticipated regions of zonal isolation from
the map of cement quality; designing a stimulating treatment based
on the presence of regions of fluid communication based on the map
of cement quality created from one or more cement logs, wherein the
designing the stimulating treatment comprises using diversion
techniques at anticipated regions of fluid communication; and
performing the stimulation treatment.
2. The method of claim 1, further comprising: characterizing a
cementing job within one or more intervals in a wellbore.
3. The method of claim 1, wherein the designed stimulating
treatment places stimulation stages at anticipated regions of zonal
isolation.
4. The method of claim 1, wherein the designed stimulating
treatment avoids placing stimulation stages at anticipated regions
of fluid communication.
5. The method of claim 1, wherein the one or more cement logs are
selected from a group consisting of cement bonding logs, variable
cement density logs, and ultrasonic cement logs.
6. The method of claim 1, wherein preparing the map of cement
quality comprises simulating mud displacement.
7. The method of claim 1, further comprising: importing the map of
cement quality into a software configured to design stimulating
operations.
8. The method of claim 1, wherein the map of cement quality is
based on presence or absence of hydraulic isolation, reservoir
quality, or completion quality.
9. A method, comprising: preparing a map of cement quality for one
or more intervals of a wellbore; comparing the map of cement
quality to a map of completion quality and a map of reservoir
quality; designing a stimulating treatment based on the maps of
cement quality, completion quality, and reservoir quality; and
performing the stimulation treatment.
10. The method of claim 9, wherein the designed stimulating
treatment comprises stimulation stages placed at regions of having
at least two of good cement quality, good completion quality and
good reservoir quality.
11. The method of claim 9, wherein the designed stimulating
treatment comprises stimulation stages placed at regions having
good reservoir quality and poor cement quality with the use of
diversion techniques where there is poor cement quality.
12. The method of claim 9, wherein the map of cement quality
comprises a simulated map based on cement displacement.
13. The method of claim 9, wherein the map of cement quality
comprises one or more cement logs selected from a group consisting
of cement bonding logs, variable cement density logs, and
ultrasonic cement logs.
Description
BACKGROUND
Following the cessation of drilling operations, completions may be
initiated in which downhole tubulars and equipment are installed to
enable the safe and efficient production from an oil or gas well.
During completions, sections of casing or pipe string may be placed
into the wellbore to enhance wall strength and minimize the chances
of collapse, burst, or tensile failure. Well casings of various
sizes may be used, depending upon depth, desired hole size, and
types of geological formations encountered. The casing and other
tubulars may, in some instances, be stabilized and bonded in
position using various physical and chemical techniques.
When cement or other settable compositions are used to stabilize
completion equipment, a portion of the drilling fluid may be
removed from the wellbore so that the casings may be cemented in
place. Primary cementing operations may fill at least a portion of
the annular space between the casing and the formation wall with a
hydraulic cement composition. The cement composition may then be
allowed to solidify in the annular space, thereby forming an
annular sheath of cement. During stimulation (such as hydraulic
fracturing or other techniques), cement may provide an impermeable
barrier that prevents the migration of stimulation fluids between
zones to be stimulated in the wellbore. In some cases, when needed,
cement may provide an impermeable barrier that prevents the
migration of undesired fluids and gases (e.g., water) between zones
penetrated by the wellbore during production. Other situations
arise where cementing particular zones within a formation may be
beneficial. For example, cementing operations may also include use
of cement during remediation of lost circulation or zonal
isolation.
SUMMARY
This summary is provided to introduce a selection of concepts that
are described further below in the detailed description. This
summary is not intended to identify key or essential features of
the claimed subject matter, nor is it intended to be used as an aid
in limiting the scope of the claimed subject matter.
In one aspect, embodiments disclosed herein relate to a method that
includes preparing a map of cement quality for one or more
intervals of a wellbore; determining anticipated regions of fluid
communication and anticipated regions of zonal isolation from the
map of cement quality; and designing a stimulating treatment based
on the presence of regions of fluid communication.
In another aspect, embodiment disclosed herein relate to a method
that includes preparing a simulated map of cement quality;
determining anticipated regions of fluid communication; and
designing a cementing operation based on the presence of
anticipated regions of fluid communication.
In yet another aspect, embodiments disclosed herein relate to a
method that includes preparing a map of cement quality for one or
more intervals of a wellbore; comparing the map of cement quality
to a map of completion quality and a map of reservoir quality; and
designing a stimulating treatment based on the maps of cement
quality, completion quality, and reservoir quality.
Other aspects and advantages of the disclosure will be apparent
from the following description and the appended claims.
BRIEF DESCRIPTION OF FIGURES
FIG. 1 is an illustration of a completions operation in which
cement is installed in an annular region created between a borehole
and an installed casing in accordance with embodiments of the
present disclosure.
FIGS. 2 and 3 are graphic depictions illustrating a fracture
operation in accordance embodiments of the present disclosure.
FIG. 4 is a schematic depicting a flow diagram in accordance with
embodiments of the present disclosure.
FIGS. 5-7 show simulated fluid concentration maps in accordance
with embodiments of the present disclosure.
FIG. 8 is a schematic showing cement quality mapping in accordance
with embodiments of the present disclosure.
FIG. 9 is a schematic of a wellbore used in designing stimulation
treatments in accordance with embodiments of the present
disclosure.
FIG. 10 is a schematic depicting a flow diagram in accordance with
embodiments of the present disclosure.
FIG. 11 is a computer system in accordance with embodiments of the
present disclosure.
DETAILED DESCRIPTION
In one aspect, methods in accordance with this disclosure are
directed to the design of completions methods that include the
characterization of cementing jobs within an interval of a
wellbore, and the design of subsequent fracturing operations. In
another aspect, methods in accordance with the present disclosure
are directed to the design of cementing jobs using modeling
techniques that estimate the degree of isolation of various regions
of the wellbore once the cement has been emplaced and cured.
Methods in accordance with the may include techniques for valuating
and determining cement hydraulic isolation, and combining the
information with formation evaluation to minimize uncertainty with
pinpoint accuracy when selecting regions for perforation and
stimulation during subsequent operational stages. In one or more
embodiments, methods may include the creation of a cement quality
map for sections of a wellbore that may be used to optimize the
formulation and placement of a cementing job and/or used to design
stimulation operations that avoid cemented regions that have low
quality or suboptimal hydraulic isolation.
In one or more embodiments, methods in accordance with the present
disclosure may include performing a cementing job, characterizing
the cementing job, preparing a map of cement quality that may
indicate regions of fluid communication in the near and far
wellbore areas, and designing a stimulating treatment based on the
obtained data. In some embodiments, methods may be executed using
computer software that optimizes the characterization of the degree
of cement isolation in one or more zones within the wellbore, and
may assist users in placement of perforations and other wellbore
stimulation techniques that minimize interzonal communication in
the near- and far-wellbore. Computer software in accordance with
the present disclosure may incorporate cement isolation
information, including generating cement quality maps for a given
wellbore.
Cementing operations may proceed by emplacing a cement within a
wellbore, such as in an annulus created between a wall of the
formation and a section of installed casing. With particular
respect to FIG. 1, a derrick 100 is shown installed on a wellbore
101 traversing a formation 102. Within the wellbore 101 casing
strings 109, 108, 107 & 104 are nested within each other.
Casing 104 was run as the last string (production casing or liner)
in preparation for installation of a cement sheath between the
outside of the casing and the exposed formation and/or other
emplaced casing strings (i.e. 107). During the cementing operation,
a cement slurry 106 is pumped into an annulus formed between
formation 102 and the casing 104. In some embodiments, cement
slurry may be pumped into multiple annular regions within a
wellbore such as, for example, (1) between a wellbore wall and one
or more casing strings of pipe extending into a wellbore, or (2)
between adjacent, concentric strings of pipe extending into a
wellbore, or (3) in one or more of an A- or B-annulus (or greater
number of annuli where present) created between one or more inner
strings of pipe extending into a wellbore, which may be running in
parallel or nominally in parallel with each other and may or may
not be concentric or nominally concentric with the outer casing
string.
During wellbore stimulation, a wellbore may be perforated in a
number of different locations in order to increase production,
either in the same hydrocarbon-bearing zone or in different
hydrocarbon-bearing zones, and thereby increase the flow of
hydrocarbons into the well. Within a single wellbore, there may be
one or more zones of interest within various subterranean
formations or multiple layers within a particular formation. With
particular respect to FIG. 2, a wellbore 202 may traverse one or
more zones of interest 204. After drilling, a casing 206 may be
lowered into the wellbore 202, and the wellbore 202 may be filled
with cement 205 to cement casing 206 in place. After the cementing
operation is complete, a perforating tool may be lowered into the
wellbore to create perforations 208 through a casing 206 and cement
cement and into the near wellbore, in order to access/stimulate the
zones of interest 204.
Stimulation may target single or multiple zones within the well at
time through the use of various technologies. For example,
stimulation may involve multiple steps such as running a
perforating gun down the wellbore to one or more target zones,
perforating the target zones, removing the perforating gun,
treating the target zones with a hydraulic fracturing fluid, and
then isolating the perforated target zones for subsequent
production. Plug and perforation operations often utilize the
installation of plugs inside the casing and/or liner to isolate a
target zone for stimulation from the remainder of the well. Plugs
and packers may be used to isolate regions of the wellbore to
minimize the risk of fracturing fluid by-passing the plug and
damaging the wellbore through overflushing at elevated pressures,
which can stimulate collateral intervals around the target.
The plug and perforation process may be repeated for all the target
zones or a subset of target zones of interest until all the target
zones are treated. However, production from multiple fractured
intervals may encounter issues with control of the flow of fluids
from the formation. For example, in a well producing from a number
of separate zones (or from laterals in a multilateral well) in
which a high pressure zone may neighbor a low pressure zone, the
higher pressure zone may disembogue into the lower pressure zone
rather than to the surface, potentially damaging the zone and
limiting production. Similarly, in a horizontal well that extends
through a single zone, having perforations near the "heel" of the
well, i.e., nearer the surface, may begin to produce water before
those perforations near the "toe" of the well. The production of
water near the heel may then reduce the overall production from the
well.
To remedy possible problems during stimulation, zones may be
isolated with various tools such as a packer 210 emplaced on a
string of tubing 212. Packers and other isolation elements such as
bridge plugs and bull plugs may restrict flow from other intervals
while stimulating a target interval. In some embodiments,
intelligent completions may be used, which involves the use of
liner systems, production packers, subsurface flow controls, and
subsurface safety valves. Modern completion systems may also
incorporate both sensing and control systems, inflow control
devices (ICDs), flow control valves (FCVs), pressure gauges, and
control lines that may allow users to drain their reservoirs with
granularity and may provide an increased feedback regarding fluid
movement and reservoir drainage.
However, the use of isolation techniques and intelligent completion
systems within the wellbore may have limited effectiveness in
situations in which the cementing job behind the casing that
isolates the sections from the formation is incomplete or
defective. Following cementing operations in normal course,
cementing characterization techniques may not consider cement
isolation following emplacement, instead considering only formation
properties, which may not reveal near-fluid communication between
intervals, which can lead to uncertainty with regard to the level
of fluid communication between zones, particularly after one or
more zones have been perforated during stimulation operations. For
example, with particular respect to FIG. 3, defects in primary
cementing jobs may result in the formation of channels and
microannuli that allow fluid communication through mud channels
left in the wellbore 202 or through cracks 304 within the cement
205. Further, depending on a number of factors, such as spacing
between fractured intervals and the nature of the formation, vugs
and other natural channels may lead to far-wellbore fluid
communication 306 as well, though, such communication may be
dependent on the formation and not a result of cement issues. Such
problems may not be evident following cementing and fracturing
operations, and cement characterization is rarely if ever performed
prior to subsequent operations. The end result then is that an
operator may underestimate the degree of fluid connectivity between
perforated intervals, which can result in issues that impact
overall production.
Methods in accordance with the present disclosure may look at zonal
isolation quality following cementing operations. In one or more
embodiments, well geometry, washout, mud quality, cements and
spacers quality, flow rates, centralization of casing string and
other variables may be used to create cement quality maps that will
be used as a predictive aid to quantify zonal isolation to enable
informed design decisions for subsequent fracturing operations. In
some embodiments, cement quality maps may be used to prepare
fracturing operations such as plug-and-perf operations to enhance
production. Cement quality maps may be used as a metric to quantify
the zonal isolation confidence factor (ZIF), which may be used with
other criteria such as reservoir quality (RQ) and completion
quality (CQ) to enable informed design decisions for subsequent
fracturing operations in some embodiments.
In one or more embodiments, evaluation logs such as open hole logs
or logging-while-drilling logs, surface measurements, cementing
placement data and cement density/bond log, variable density log,
and/or ultrasonic cement log (such as from a USI.TM. UltraSonic
Imager Tool or by IsolationScanner.TM., both of which are
commercially available from Schlumberger Technology Corporation)
may be correlated and analyzed in a single workflow (such as
INVIZION EVALUATION.TM., available from Schlumberger Technology
Corporation) to create a cement quality map. In some embodiments,
cement quality maps may provide a quantitative or qualitative
estimation of the ZIF. In some embodiments, ZIF may be expressed in
binary terms, and indicate whether hydraulic isolation is present
or not present, i.e., whether there is good or poor cement quality.
In some embodiments, ZIF may be expressed as a likelihood of
hydraulic isolation, such as percent confidence of hydraulic
isolation in the range of 0% to 100%.
In one or more embodiments, methods may be directed to integrated
cement evaluation techniques that may consider a number of factors
prior to and following placement of a cement composition within a
wellbore. Methods in accordance with the present disclosure may
include the creation and design of cement quality maps that may
guide the user during the cement formulation and installation
process in some embodiments, and/or cement quality maps may be
generated from cement logs of an existing cement job and used to
design subsequent stimulation operation. Relevant data used to
generate cement quality maps in accordance with the present
disclosure include open hole data, post placement cement forecasts,
cased hole evaluations, cementing placement data and cement
density/bond log, variable density log, and/or ultrasonic cement
log (such as from a USI.TM. UltraSonic Imager Tool or by
IsolationScanner.TM., both of which are commercially available from
Schlumberger Technology Corporation).
Methods in accordance with the present disclosure may optimize
wellbore stimulation operations by analyzing cement isolation data
when evaluating stimulation treatment design data and performing
calibration based on determined conditions in the wellbore such as
pressure and temperature. Methods in accordance with the present
disclosure may consider a number of factors regarding emplaced
cement jobs such as the quality of the bond to the casing, the
anticipated level of hydraulic communication during subsequent
wellbore operations including stimulation and fracturing, and the
like.
Methods in accordance with the present disclosure may deliver
cement evaluations with a reduced level of uncertainty as to the
level of hydraulic isolation and may be used to calibrate formation
data with pinpoint accuracy. In some embodiments, methods may
include cement emplacement and stimulation design according to the
results of the cement isolation characterization.
In one or more embodiments, cement characterization techniques may
be reactive and focused on characterizing an existing cementing job
prior to aiding in the design and execution of a stimulation
operation. In some embodiments, hydraulic isolation may be
characterized in conjunction with other formation evaluation
techniques and used to design stimulation operations, including
placement of perforations and completions design. Cementing
characterization techniques may be developed from open-hole data,
post-placement cement forecasts, and the like. In some embodiments,
information obtained from cement hydraulic isolation
characterization may be used with other information used in the
design of stimulation treatments including open-hole and cased-hole
evaluations, wellbore geometry, and formation properties.
In embodiments in which cement quality maps are incorporated into a
wellbore operation design suite, cement quality maps may define the
condition of cement sheath behind the casing, such as the degree of
hydraulic isolation along the wellbore, and enable users to
consider cement quality in addition to relevant formation
properties when determining the placement of perforations in
fracturing operations. In some embodiments, formation
characterization may be calibrated with pinpoint accuracy,
minimizing uncertainty related to concerns about cement isolation
and allowing targeted placement of perforations and other
stimulation treatments.
In one or more embodiments, field completion plans may be optimized
based on updated stimulation/formation data obtained following a
cement job. During cementing operations, intervals within a
wellbore, such as in a horizontal section, may have insufficient
standoff (i.e. centralization of a casing string in wellbore),
which may create fingering and channeling of a cement-forming
slurry that results in porous structures that enable fluid
communication. Cementing jobs may also be modified in some
embodiments through the installation of agitators, such as
turbolizers, or centralizers within selected zones to minimize
channel formation, or through the use of practices such as
reciprocation, rotation, and/or vibration of the casing string to
minimize channel formation.
In some embodiments, methods may involve selecting fracturing
stages along the wellbore above or below plug depths or between
cemented sleeves where cement isolation is acceptable. Methods in
accordance with the present disclosure may also involve the design
of preparatory and remediating treatments for stimulation treatment
stages. For example, diversion treatments such as fiber pills or
chemical diverters may be used to treat near- or far-wellbore fluid
and pressure loss prior to or during stimulation treatments.
With particular respect to FIG. 4, a flow diagram of a stimulation
design method in accordance with the present disclosure is shown.
During the initial stages, formation variables are collected at 402
from a number of sources including information from
logging-while-drilling, cuttings analysis, acoustic and radioactive
measurements, and the like. Next, primary cementing is performed at
404 following the installation of tubulars (e.g. casing string) and
other wellbore equipment. Once primary cementing is completed, the
cementing job is characterized at 406 using an appropriate
technique such as a cement density/bond log, variable density log,
and/or ultrasonic cement log (such as from a USI.TM. UltraSonic
Imager Tool or by IsolationScanner.TM., both of which are
commercially available from Schlumberger Technology Corporation),
and a map of cement quality is generated. However, in other
embodiments, the cementing job is characterized at 406 based on the
computer simulation of mud cleaning/displacement and the cement
slurries being pumped to generate a cement quality map. It is also
envisioned that the computer simulations may be used in combination
with cement logs. The cement quality map may then inform the
stimulation job design at 408, which may include importing the
cement quality map into stimulation design software. The
stimulation job is then designed, taking into account, for example,
the presence of cemented intervals that may have less than optimal
levels of expected hydraulic isolation when planning the placement
of perforations, or decision on opening or not frac valves, packers
and other equipment to minimize complications in later production
operations. That is, if a particular interval has less than
desirable cement quality to achieve zonal isolation (but acceptable
quality above and below the interval), the stimulation may be
designed (or modified) to stimulate such interval (e.g. to adjust a
depth of perforation interval or decision on opening or not frac
valves or sliding sleeves).
After the quality of the cementing job has been appraised or the
cement quality map considered, stimulation operations may be
designed, for example, using diversion or sequential fracturing
techniques of any type (such as, but not limited to use of sliding
sleeves such as with BROADBAND.TM. services available from
Schlumberger Technology Corporation, frac plugs such as with
Plug-and-Perf services available from Schlumberger Technology
Corporation, degradable frac balls, etc.). However, it is also
envisioned that other fracturing techniques may be used.
Stimulation design may involve setting the number and distance
between the perforations for each perforation stage, which may
involve placement of perforations or wellbore bridge plugs at
regions having acceptable hydraulic isolation. Given that some of
such techniques involve installation of the completion equipment
prior to pumping the cement, use of a predictive cement quality map
(based, for example, on mud displacement) may aid in the selection
and placement of the completion equipment within the well.
During stimulation operations, pressure, temperature, and fluids
may be monitored to determine the presence of fluid communication
between stages, including near and far field effects. In addition,
wellbore clean out may be monitored for the presence of sands in
some embodiments. In some embodiments, wellbore cleanout may be
monitored for the presence of sand. For example, the presence of
sand may be correlated with poor zonal isolation where fluid
communication exists above and below an installed packer and may
indicate that injected fluids may enter other regions beyond that
targeted.
Other evidence of fluid communication between zones may include
data from production monitoring. For example, the contribution of
fracture clusters to production may be monitored for poor
production, which may be an indication that formation fluids were
being produced elsewhere for any number of reasons such as poor
zonal isolation for stimulation or that proppant installation was
unsuccessful due to leakoff. Production monitoring may involve
monitoring data from pressure measurements and changes, logging
cleanout, production logs, and spinner logs for fluid composition
changes such as the introduction of water and brines. In addition,
changes in pressure and temperature that may also indicate fluid
communication with other zones. In some embodiments, fluid
communication may be compared to that predicted from post-job
displacement simulation software such as WELLCLEAN.TM. (WELLCLEAN
II.TM., WELLCLEAN III.TM.), 3D APERTURE.TM., and CEMENTICS.TM.
available from Schlumberger Technology Corporation.
In one or more embodiments, data obtained before and during
stimulation operations may be analyzed to determine the existence
and level of fluid communication between wellbore stages, including
near-wellbore and far-field effects. In some embodiments, fluid
communication between wellbore stages may be compared with the
results of a number of wellbore evaluation techniques including
cement evaluation logs captured from ultrasonic imaging tools,
isolation scanners, cement bonding logs, variable density logs, and
the like.
Methods in accordance with the present disclosure may integrate the
analysis of cementing job quality with the stimulating operations,
including perforation and fracture design. In one or more
embodiments, cement evaluation techniques may be used to develop a
cement quality map that may be incorporated into downstream
software used to design fracturing operations. Inputs used to
develop cement quality maps may be generated from cement quality
logs such as cement bonding logs (CBL), variable density logs
(VDL), ultrasonic logs and the like. Other inputs for developing
cement quality maps may include simulated logs of anticipated
cement quality such as synthetic CBL or simulations of
displacement.
Predictive methods in accordance with the present disclosure may
also include computer simulation of mud cleaning prior to primary
cementing, which may estimate the degree of mud removal based on
existing wellbore equipment, mud characteristics, injected fluid
composition and flow properties, and the like. Methods may include
simulations of treatments such as post-placement treatment that may
include the use of annular displacement simulation software such as
WELLCLEAN.TM. (WELLCLEAN II.TM. WELLCLEAN III.TM.), 3D
APERTURE.TM., and CEMENTICS.TM. available from Schlumberger
Technology Corporation. WELLCLEAN.TM. is a numerical cement
placement simulator uses computational fluid dynamics to design the
process of cement placement. For example, referring now to FIG. 5,
a simulation may generate a fluids concentration map, showing a
mapping of fluids (such as mud, water, spacer fluid, and cement) in
the well based on well geometry and trajectory, downhole fluid
properties, volumes, pump rates and casing centralization. Thus,
with such simulation, users may predict the efficiency of mud
removal and identify whether a mud channel will remain. In some
embodiments, the output from software such as WELLCLEAN.TM. may
also be compared to a map of stimulations sleeves for verification.
3D APERTURE.TM. simulates the mud displacement in three dimensional
space. The simulator resolves azimuthal flows around the full
annulus allowing simulation of gravity-induced segregated flow in
horizontal and deviated wells, such as that shown in FIG. 6.
Further, it is also envisioned that a three-dimensional fluid
concentration map may be broken out into each of the fluid phases
present, as shown in FIG. 7. These fluid concentration maps,
showing simulations of mud displacement may be predictive cement
quality maps in accordance with the present disclosure.
Predictive methods in accordance with the present disclosure may
allow users to adjust cement design to ensure hydraulic isolation
around zones targeted for completions, minimize fluid connectivity
following perforations, and minimize plugging and other production
issues. Adjustments to a planned cementing job may include
modifying the number of cementing stages, placement of centralizers
and other equipment for smart installation techniques, or changing
the fluid's design including rheological properties, thickening
time, compressive strength, free fluid, fluid loss and
compatibility with other fluids. In some embodiments, a synthetic
cement quality map may be generated based on formation properties
and cement composition. Synthetic cement quality maps may be
integrated into completion design software in some embodiments and
used to determine whether the cementing job will be sufficient or
should be modified or upgraded.
Other factors that may be considered in cementing design include
fluid rheology, torque, and drag when installing equipment such as
centralizers and tubing, the presence of completion hardware such
as sleeves and screens, fluid flow during mud removal, the need for
remedial measures such as pills and diverters, and the like.
Cementing operation design may also include factors such as market
pricing, material properties, component availability, operating
conditions, chemical compatibilities, and the like.
In one or more embodiments, predictive modeling techniques may
include constructing a model prior to a cementing job, calibrating
the model to pressure and rate measured or anticipated in a target
interval, and interpreting existing formation evaluation logs. In
some embodiments, predictive or "synthetic" cement quality maps may
be used to select types of cements based on formation properties
and wellbore logs. For example, in some embodiments, completions
design may be adjusted based on available cement quality or based
on performance at pressures and temperatures in a given wellbore
interval.
In one or more embodiments, software suites may be used to analyze
logs or simulate cementing results to create synthetic cement
quality maps. In one or more embodiments, synthetic cement quality
maps may be generated using commercial cementing software such as
CEMCAST.TM. and displacement simulation software such as
WELLCLEAN.TM. (WELLCLEAN II.TM., WELLCLEAN III.TM.), 3D
APERTURE.TM., and CEMENTICS.TM. available from Schlumberger
Technology Corporation, and programs that generate visual log
measurements and model the output of cement quality including the
MANGROVE.TM. plugin for PETREL.TM., all of which are available from
Schlumberger Technology Corporation.
Further, in one or more embodiments, the cement quality maps may
incorporate predictive simulations in combination with cement logs
as well as other well quality maps to produce a comprehensive
cement quality map within a single workflow, (such as INVIZION
EVALUATION.TM., available from Schlumberger Technology
Corporation). For example, referring to FIG. 8, an example of such
single workflow is shown. FIG. 8 includes well quality tracks 1-6,
cement design and placement simulation tracks 7-11, and cement
evaluation tracks 12-20. Specifically, related to well quality,
track 1 includes a gamma ray log, track 2 includes a density and
porosity log, track 3 includes a formation temperature log, track 4
includes pore pressure/fracture gradient, track 5 includes well
geometry (inclination, azimuth, and dog legs), and track 6 includes
borehole shape. Related to cement design and placement simulation,
track 7 includes a well schematic, track 8 includes standoff at
centralizers, track 9 includes fluid coverage (including muds,
spacers, slurries, etc.), track 10 includes a fluid concentration
map (including muds, spacers, slurries, etc.), and track 11
includes a risk of mud on wall. Related to cement evaluation logs,
track 12 includes a cement bond log (at both 0 and 1500 psi), track
13 includes a variable density log (at 0 psi), track 14 includes a
variable density log (at 1500 psi), and tracks 15-20 include
acoustic impedance maps.
In one or more embodiments, fluid communication between zones may
be quantified, which can provide estimates in the degree of
production decrease and fluid diversion rates between zones. For
example, the communication between stages may be compared with
production data in order to determine the change in overall
production rates and whether remediation or intervention is
necessary. In some embodiments, zonal isolation quality may be
characterized by a bond index describing the degree of cement
bonding, defined herein as a "bond index" (BI), between the casing
and formation, or between concentric casings in some cases. BI
values in accordance with the present disclosure may range from 0%,
representing no bond between cement and casing and no hydraulic
isolation, to 100%, representing complete cement bonding and
hydraulic isolation. Based on application requirements, an operator
may subdivide the BI into various subranges such as acceptable and
unacceptable. For example, in some embodiments, acceptable BI
values may be in the range of 80% to 100%, however, depending on
the application, the acceptable range of BI values may be broader
or narrower.
In one or more embodiments, characterization of hydraulic isolation
may involve determining the level of cement quality from a number
of factors such as bond index, which may be based on CBL readings,
along with other information sources such as VDL data, and output
from ultrasonic tools that include USIT, ISOLATIONSCANNER.TM., and
the like. In some embodiments, cement quality factors may be
derived from open hole or LWD evaluation logs, surface
measurements, cementing placement data, and cement bond logs, or a
subset or mixtures thereof, and may be correlated and analyzed in
single workflow to determine the hydraulic isolation quality.
In one or more embodiments methods in accordance with the present
disclosure may involve the design of single and multistage
fracturing treatments that consider formation properties and cement
quality behind installed casing. In some embodiments, stimulation
treatments may be designed such that fracturing stages are placed
in wellbore regions having known degrees of hydraulic isolation
behind the casing, including at, above, and below the stage in some
cases. In some embodiments, stimulation design may involve
sequential fracturing operations such as BROADBAND.TM. sequential
fracturing services available from Schlumberger Technology
Corporation, or the use of diverters and other treatments including
fiber and/or particulate pills, chemical treatments, and the like
to prevent fluid communication between zones during
stimulation.
In one or more embodiments, stimulation design data may be
optimized by considering cement isolation data and formation
information obtained from log data, pressure measurements,
temperature, and other factors. For example, fluid communication
between stages, including from near- and far-field wellbore
regions, which may in turn be used to estimate cement quality and
may inform placement of fracturing stages. Fluid communication
measured between stages by, for example, monitoring pressure and
temperature changes may be compared with cement evaluation logs
such as ultrasonic imaging techniques such as Schlumberger's
ISOLATION SCANNER.TM., cement bond logs, and variable density logs.
In one or more embodiments, fluid communication between stages may
be analyzed following primary cementing operations from simulations
created using specialized oilfield software such as 3D
APERTURE.TM..
Methods in accordance with the present disclosure may use
commercially available cementing software such as INVIZION.TM. or
similar. Wellbore simulations may be conducted on software such as
WELLCLEAN II.TM. WELLCLEAN III.TM., 3D APERATURE.TM., CEMENTICS.TM.
(all of which are available from Schlumberger Technology
Corporation) or similar that is capable of using inputs that can
correlate the state of wellbore (diameter, washouts, and the like)
and centralization prediction such as caliper logs, synthetic
caliper log, or any other log providing similar information
regarding the status of the wellbore.
In one or more embodiments, wellbore-specific software suites may
be used to generate a cement quality map from one or more logs and
simulation results. In some embodiments, cement quality maps may be
stored in a common database using commercial software packages such
a STUDIO.TM.. Cement quality maps may then be accessed by
fracturing design software to access the cement quality maps, which
may provide a user with information regarding cement quality during
the design of single and multistage fracturing treatments.
In one or more embodiments, methods in accordance with the present
disclosure may be proactive, involving the design of a cementing
job prior to emplacement and, in some cases, characterization of
the cementing job prior to stimulation operations. In some
embodiments, cementing operations may be optimized to ensure
adequate strength and coverage within an annulus to prevent
hydraulic communication between zones, and to withstand the forces
exerted on the casing during stimulation.
In one or more embodiments, cement quality may be estimated
predictively, prior to primary cementing. In some embodiments,
cement quality maps may be estimated using know properties of the
wellbore and installation equipment. Predictive methods of
cementing may employ predictive models that generate an anticipated
cement quality map from known wellbore data such as wellbore
geometry and formation quality, and from equipment properties and
variables such as pumping data and fluid characteristics. For
example, by using information generated prior to and during
drilling operations, the need to take cement logs following cement
emplacement may be obviated in some embodiments, which may be
advantageous in scenarios in which cement remediation will not be
performed prior to initiating fracturing operations.
Methods in accordance with the instant disclosure may be applied to
horizontal or sub-horizontal wells, including those with
multi-stage fracturing completion. During cementing operations,
isolation equipment such as packers and plugs may be installed
within a wellbore, which may create isolated zones around sleeves
in the tubing delivering a cement-forming slurry. Centralizers and
other equipment to prevent tubulars and casing from contacting
wellbore walls and other tubing may also be installed, particularly
in the case of horizontal wells, to ensure adequate cement
coverage. In some embodiments, methods in accordance with the
present disclosure may utilize cement placement software to
optimize the number of centralizers and other cementing equipment
to enhance hydraulic isolation, which may include placement of
equipment near anticipated perforation sites and other areas to
improve cement installation.
In some embodiments, methods may reduce the total amount of
centralizers without decreasing the degree of hydraulic isolation
surrounding fracturing stages. Centralizer installation may be
driven by plug or sleeve location in some embodiments, which may
increase the likelihood of cement isolation in regions in which
casing walls will be perforated and more susceptible to fluid
communication between poorly cemented zones. In one or more
embodiments, design parameters for cementing in accordance with the
present disclosure may include having at least 5 casing joints
centralized, where 2.5 joints reside above the plug and 2.5 joints
reside below the plug, placing centralizers at a density of 2
centralizers per 1 joint. In some embodiments, centralizers and
other supports may be provided in regions in which perforations
will be located, proving a standoff 2.5 joints below the plug and
2.5 joints above a plug or packer. In some embodiments, a
turbolizer may be combined with a normal centralizer, or a
single-piece centralizer-turbolizer may be used on the first joint
of the interval (if counted from the bottom), and combining
centralization with casing movement technique.
Further, as mentioned above, cement quality maps of the present
disclosure may be used as a metric to quantify the zonal isolation
confidence factor (ZIF), which may be used with other criteria such
as reservoir quality (RQ) (if the reservoir is good enough to be
fracked, i.e., whether hydrocarbons are present) and completion
quality (CQ) (whether the rock is conducive to being stimulated,
considering, for example, mechanical prop of rock, Young's modulus,
compressive strength, etc.) to enable informed design decisions for
subsequent fracturing operations in some embodiments. Thus, for
example, depending on the level of acceptable ZIF (between 0-100%),
a stimulation operation may be designed not only based on the ZIF,
but also considering the reservoir quality and the completion
quality, as shown, for example, in FIG. 9. While the most desirable
job would entail good ZIF, good RQ, and good CQ, the number of
stages or clusters that would result from such requirement may not
be adequate depending on the well. Thus, stimulations may be
prioritized to choose from those where each of ZIF, RQ, and CQ are
good, and secondly, where two of ZIF, RQ, and CQ are good, thirdly,
where one of ZIF, RQ, and CQ are good and generally avoiding where
none of ZIF, RQ, and CQ are good.
In one or more embodiments, predictive methods may consider the
initial wellbore condition following drilling operations and before
primary cementing. In some embodiments, methods may be used to
select and emplace cement within the wellbore. With particular
respect to FIG. 10, a flow diagram for an embodiment of a method is
shown in which information about the formation is used to design an
optimized cementing job. During the initial stages, wellbore data
is collected at 1002 from a number of sources including information
from logging-while-drilling, cuttings analysis, acoustic and
radioactive measurements, calipers, and the like. This information
may include, for example, wellbore geometry, washout, etc. In
addition, information may be collected regarding the type of cement
used and other variables such as set time, particle size, the
presence of hydration inhibitors or accelerants, the presence of
structural additives such as fibers and particulates, and the
like.
At 1004, an initial cement job is designed based on the expected
wellbore, which may include, for example, a pumping schedule,
cement formulations, spacers, surfactant packages, and orders of
component addition. Based on the initial design, simulations of
cement placement within the wellbore are performed using
appropriate modeling software. In one or more embodiments, methods
of designing a cementing job may also include simulation of torque
and drag within the wellbore to determine the ability of running
casing to the bottom of the wellbore with the selected centralizer
setup. The available information may be used to construct a
simulated or synthetic cement quality map at 1006 in some
embodiments, which may anticipate regions of fluid communication in
one or more of a near-wellbore region and a far-wellbore region if
present. Cement quality maps are then used at 1008 to adjust the
design of the cementing job including, for example, a pumping
schedule, cement formulations, spacers, surfactant packages, and
orders of component addition. In some embodiments, cement job
design (and adjustment thereof) may also include the placement of
cementing equipment such as tubulars, centralizers, and the like,
and may evaluate the hierarch of friction and pressure within the
system, allowing for the adjustment of piping diameter, the types
of pumps required to deliver cement slurry, and similar
factors.
Following adjustment of the cementing job design, the job may be
performed at 1010 and, in some embodiments, evaluated using various
logging and predictive techniques to ensure that installation
occurred as planned and to verify the quality of hydraulic
isolation. In some embodiments, the synthetic cement quality map
generated at 1006 may also be used to design stimulation treatments
at 1014 with or without further characterization of the emplaced
cement job using cement logs and the like at 1012. However, it is
also envisioned that a second cement quality map that incorporates
the cement logs may be generated. The stimulation job may then be
designed at 1014, including the placement of perforations, or
decision on opening or not frac valves, packers and other equipment
to minimize complications in later production operations. Such
design may be based on the first and/or second cement quality map.
Following stimulation job design, the job may be evaluated for
feasibility and initiated at 1016.
Thus, embodiments of the present disclosure include both proactive
and reactive completion and stimulation designs. In the proactive
setting, predictive cement quality maps (alone or in combination
with other factors such as RQ and CQ) may be used to assess whether
the expected outcome will be sufficient or whether to modify the
cement job design itself, such as through modifying the fluids,
flows, casing reciprocation/rotation/vibration, centralization,
etc. based on desired stimulation stages (for the RQ and CQ). Thus,
desired stimulation based on RQ and CQ is used to modify the cement
design through the use of the predictive cement quality maps. In a
reactive design, cement quality maps (including either predictive
maps or cement logs) may be used to design the stimulation
treatment to avoid, for example, regions where fluid communication
is anticipated. Rather, stimulation stages are desirably placed in
regions of good cement quality. Further, when RQ is good, but ZIF
is poor, it is envisioned that the stimulation techniques may be
selected to overcome the poor cement quality (such as those
involving a higher investment through the use of diversion
techniques, etc.).
Cement Compositions
Cement compositions in accordance with the present disclosure may
include cements, resins and other settable materials. Cement
compositions may include mixtures of lime, silica and alumina, lime
and magnesia, silica, alumina and iron oxide, materials such as
calcium sulphate and Portland cements, and pozzolanic materials
such as ground slag, or fly ash. Formation, pumping, and setting of
a cement slurry is known in art, and may include the incorporation
of cement accelerators, retardants, dispersants, etc., as known in
the art, so as to obtain a slurry and/or set cement with desirable
characteristics.
In a particular embodiment, cement compositions may incorporate a
magnesium-based cement such as a "Sorel" cement. Magnesium-based
cements are fast setting cements that approach maximum strength
within 24 hours of contact with water. While not limited by any
particular theory, the cement-forming reaction mechanism is thought
to be an acid-base reaction between a magnesium oxide, such as MgO,
and available aqueous salts. For example, mixing solid MgO and a
brine containing MgCl.sub.2 results in an initial gel formation
followed by the crystallization of the gel into an insoluble cement
matrix, producing magnesium oxychloride (MOC) cement. Other
magnesium-based cements may be formed from the reaction of
magnesium cations and a number of counter anions such as, for
example, halides, phosphates, sulfates, silicates,
aluminosilicates, borates, and carbonates. In some embodiments,
anions may be provided by a magnesium salt of the selected
anion.
In addition to MOC cements, prominent examples of magnesium-based
cements also include magnesium oxysulfate (MOS) cements formed by
the combination of magnesium oxide and a magnesium sulfate
solution), and magnesium phosphate (MOP) cements formed by the
reaction between magnesium oxide and a soluble phosphate salt, such
as ammonium phosphate (NH.sub.4H.sub.2PO.sub.4). Other suitable
magnesium cements may also include magnesium carbonate and
magnesium silicate cements. In one or more embodiments, magnesium
cements may also include combinations of any magnesium cements
described herein and those known in the art.
In other embodiments, the cement composition may be selected from
hydraulic cements known in the art, such as those containing
compounds of calcium, aluminum, silicon, oxygen and/or sulfur,
which set and harden by reaction with water. These include
"Portland cements," such as normal Portland or rapid-hardening
Portland cement, sulfate-resisting cement, and other modified
Portland cements; high-alumina cements, high-alumina
calcium-aluminate cements; and the same cements further containing
small quantities of accelerators or retarders or air-entraining
agents. Other cements may include phosphate cements and Portland
cements containing secondary constituents such as fly ash,
pozzolan, and the like. Other water-sensitive cements may contain
aluminosilicates and silicates that include ASTM Class C fly ash,
ASTM Class F fly ash, ground blast furnace slag, calcined clays,
partially calcined clays (e.g., metakaolin), silica fume containing
aluminum, natural aluminosilicate, feldspars, dehydrated feldspars,
alumina and silica sols, synthetic aluminosilicate glass powder,
zeolite, scoria, allophone, bentonite and pumice.
In one or more embodiments, the set time of the cement composition
may be controlled by, for example, varying the grain size of the
cement components, varying the temperature of the composition, or
modifying the availability of the water from a selected water
source. In other embodiments, the exothermic reaction of components
included in the cement composition (e.g., magnesium oxide, calcium
oxide) may be used to increase the temperature of the cement
composition and thereby increase the rate of setting or hardening
of the composition.
Cement compositions may also include a variety of inorganic and
organic aggregates, such as saw dust, wood flour, marble flour,
sand, glass fibers, mineral fibers, and gravel. In some
embodiments, a cement component may be used in conjunction with set
retarders known in the art to increase the workable set time of the
cement. Examples of retarders known in the art include
organophosphates, amine phosphonic acids, lignosulfate salts,
hydroxycarboxylic acids, carbohydrates, borax, sodium pentaborate,
sodium tetraborate, or boric acid, and proteins such as whey
protein.
Embodiments of the present disclosure may be implemented on a
computing system. Any combination of mobile, desktop, server,
embedded, or other types of hardware may be used. For example, as
shown in FIG. 11, the computing system (1100) may include one or
more computer processor(s) (1102), associated memory (1104) (e.g.,
random access memory (RAM), cache memory, flash memory, etc.), one
or more storage device(s) (1106) (e.g., a hard disk, an optical
drive such as a compact disk (CD) drive or digital versatile disk
(DVD) drive, a flash memory stick, etc.), and numerous other
elements and functionalities. The computer processor(s) (1102) may
be an integrated circuit for processing instructions. For example,
the computer processor(s) may be one or more cores, or micro-cores
of a processor. The computing system (1100) may also include one or
more input device(s) (1110), such as a touchscreen, keyboard,
mouse, microphone, touchpad, electronic pen, or any other type of
input device. Further, the computing system (1100) may include one
or more output device(s) (1108), such as a screen (e.g., a liquid
crystal display (LCD), a plasma display, touchscreen, cathode ray
tube (CRT) monitor, projector, or other display device), a printer,
external storage, or any other output device. One or more of the
output device(s) may be the same or different from the input
device(s). The computing system (1100) may be connected to a
network (1112) (e.g., a local area network (LAN), a wide area
network (WAN) such as the Internet, mobile network, or any other
type of network) via a network interface connection (not shown).
The input and output device(s) may be locally or remotely (e.g.,
via the network (1112)) connected to the computer processor(s)
(1102), memory (1104), and storage device(s) (1106). Many different
types of computing systems exist, and the aforementioned input and
output device(s) may take other forms.
Software instructions in the form of computer readable program code
to perform embodiments of the invention may be stored, in whole or
in part, temporarily or permanently, on a non-transitory computer
readable medium such as a CD, DVD, storage device, a diskette, a
tape, flash memory, physical memory, or any other computer readable
storage medium. Specifically, the software instructions may
correspond to computer readable program code that when executed by
a processor(s), is configured to perform embodiments of the
invention.
Further, one or more elements of the aforementioned computing
system (1100) may be located at a remote location and connected to
the other elements over a network (1112). Further, embodiments of
the invention may be implemented on a distributed system having a
plurality of nodes, where each portion of the invention may be
located on a different node within the distributed system. In one
embodiment, the node corresponds to a distinct computing device.
However, the node may correspond to a computer processor with
associated physical memory. The node may also correspond to a
computer processor or micro-core of a computer processor with
shared memory and/or resources.
Although the preceding description has been described herein with
reference to particular means, materials and embodiments, it is not
intended to be limited to the particulars disclosed herein; rather,
it extends to all functionally equivalent structures, methods and
uses, such as are within the scope of the appended claims. In the
claims, means-plus-function clauses are intended to cover the
structures described herein as performing the recited function and
not only structural equivalents, but also equivalent structures.
Thus, although a nail and a screw may not be structural equivalents
in that a nail employs a cylindrical surface to secure wooden parts
together, whereas a screw employs a helical surface, in the
environment of fastening wooden parts, a nail and a screw may be
equivalent structures. It is the express intention of the applicant
not to invoke 35 U.S.C. .sctn. 112(f) for any limitations of any of
the claims herein, except for those in which the claim expressly
uses the words `means for` together with an associated
function.
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